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Google enhances WebP to take on PNG

Google has enhanced its open source image format WebP. The latest update adds a new lossless compression technology and supports transparency information for images. This, the developers say, allows the format to be an alternative to PNG; it was originally introduced as an alternative to JPEG, with its lossy compression of image files promising files up to 39 per cent smaller but retaining the same quality. PNG, a very popular image format for the web, is the target for the Google developers now, especially with the support for transparency.

According to Google, the new lossless mode has given results in tests (with lossless PNG files taken from around the web) of up to 45 per cent smaller files. If the PNGs are recompressed with pngcrush and pngout, WebP still offers a 28 per cent reduction in size. The new transparency mode is also said to be more efficient as it losslessly compresses only the alpha channel, adding only 22 per cent over lossy WebP encoding at quality 90. A study and a gallery offer opportunities to compare the new modes.

WebP is based on the open video format WebM's single image compression for intra-frame coding which is then encapsulated within a RIFF (Resource Interchange File Format) container. Recently, the developers introduced support for animation, ICC profiles, XMP metadata and tiling. Browsers that support WebP include Google Chrome, Google Chrome Frame, Chromium, Opera and Android 4.0/ICS's native browser. Converters for converting PNG and JPEG formats are available for Windows, Mac OS X and Linux, along with a standalone codec for Windows, and source code.